Recently, in the field of automobiles that places importance on comfortability and fuel efficiency, fine surface roughness of a gear used for a transmission or the like to achieve less noise, less vibration and lower fuel consumption has been increasingly demanded.
To achieve fine surface roughness of a gear, a conventional technique is such that the gear and a threaded grindstone are mutually rotated in engaging relation for generation grinding of a tooth flank of the gear (refer to, for example, Patent Document 1).